Google launches Project Fi: A pay for what you use voice and data plan

As expected. Google launched its mobile phone service for voice and data use on Wednesday. Called Project Fi. the plan is available on an invite-only basis and works solely with Google's Nexus 6 Android phone. Service will be made available through Sprint's and T-Mobile's networks.

Project Fi will rely heavily on Wi-Fi networks to help keep costs down, both for Google and for users of the plan. When you're connected to Wi-Fi, for example, all of your voice and data activities will use that network. Leave the Wi-Fi behind and service will migrate over an LTE mobile broadband, using what Google determines is the faster of the two carrier networks, depending on your location.

Google says that the transition between Wi-Fi and mobile broadband networks is seamless; something I'm looking forward to testing. The company also encrypts data on Wi-Fi networks, which is one of the benefits a carrier connection

typically provides.

What's Hot on ZDNet

The plan -- there's only one -- is meant to be simple and also provide a solid value to consumers. The base cost is $20 per month, which covers all voice minutes, texts, Wi-Fi tethering and international coverage in more than 120 countries. There's a flat add-on fee for cellular data, priced at $10 per GB.

Since most people don't use their full monthly data allocation, Google will credit back any unused data. Spending $30 for 3GB of data but only using 1.4GB in that month would result in a $16 credit, Google says.

One interesting aspect that reminds me of Google Voice, where I have a custom phone number, is that your Project Fi phone number "lives in the cloud." That allows you to use a phone, tablet or browser with Project Fi and have conversations regardess of the device you're using.